A British boarding school education has become a "must-have" for the children of growing numbers of the international elite living everywhere from Russia and Germany to Hong Kong.
But as oligarchs and tycoons thumb through brochures of luxurious boarding houses, a new breed of canny parent is emerging, one who is seeking a "discount option". These parents are shunning boarding schools in favour of lodging their children in private homes and sending them to day schools.
Homestay packages - including guardianship, school fees and airport transfers - can cost between pound;18,000 and pound;24,000, while full boarding at a top school now commands fees of up to pound;33,000 a year.
Hilary Moriarty, national director of the Boarding Schools' Association, said the phenomenon could pose a threat to vulnerable boarding schools, which increasingly rely on the overseas market to boost numbers.
As well as the lower costs, parents were attracted by the prospect of their child staying with a British family, rather than mixing with fellow overseas students in a boarding house and failing to learn the language, she said. The arrangement is currently most popular with the Chinese: half of day-school overseas pupils whose parents live abroad are from China.
Ms Moriarty was also concerned that UK boarding numbers could come under threat from competitor countries such as the US, Canada, Australia and New Zealand. The Antipodean nations were particularly well-placed to serve the booming Asian market, she explained.
The UK, meanwhile, could struggle to compete because of the government's "schizophrenic" attitude to immigration. Whereas the Department for Business, Innovation and Skills actively advertised for foreigners to come to the UK, Home Office policies had become increasingly unwelcoming, Ms Moriarty said.
Private boarding schools in the UK are hugely popular with foreign parents, with more than 23,000 non-British pupils enrolled whose parents live overseas. More than 4,660 pupils come from Hong Kong, more than 3,880 from mainland China and nearly 2,500 from Russia.
On the issue of homestays, Ms Moriarty said: "Everybody sees that as a market which is likely to grow because you are getting a boarding education and not paying a boarding fee.
"If somebody can access the education that they seek and get it cheaper - live in this country more cheaply - I do think that's a threat to boarding. It may be that this is absorbing a new market. Historically, it may have been that you had financially extremely well-off families able to afford it, but it may be this kind of cut-price offer is attractive to a different market."
But she claimed that although the "sales pitch" by agencies who set up homestays would emphasise the benefits, such as better language learning and a "homely" environment, families wouldn't necessarily "know what they're getting".
At present, anyone can offer guardianship services, and a campaign is under way by well-established companies in the field calling for further regulation.
For the first time this year, the Independent Schools Council measured the numbers of overseas pupils in day schools whose parents lived abroad. Almost 500 of a total 1,089 were from mainland China.
Duncan Hume, founder of White House Guardianships, said the popularity of homestays varied considerably between nationalities. "In some cases, homestay is a second best; you would never sell it to a Russian, for example, as they want to show off to their friends that they can afford boarding," he added. "I don't feel the day-school option is competing with boarding because if people could afford boarding they would do it."
He added that, alongside economic reasons, parents were choosing homestays so that their children could attend academically elite schools while also mixing with people who were not overseas students.
"In schools with big foreign communities, unless the school is vigilant, the kids don't learn any English at all," he explained. "I know of one Chinese boy who went to boarding school and never ate in the canteen. He cooked noodles in his room and came back home with no better English than when he went."
Ms Moriarty raised concerns about homestays just weeks after it was reported that foreign families were paying up to pound;10,000 a year for guardianship services while their children studied at popular British state schools. Pupils attend for around one year in most cases, living with a host family in the catchment area, but some remain for much longer.